Thainop wrote: I tried typing before posting here, it wasn't working then.
You probably forgot the "sudo" bit. When it spits out the message "you must manually run 'dpkg --configure -a' to correct the problem." you are most likely already running the installer as superuser 'root' so it doesn't mention "sudo" ... And then when you --now a normal user again-- try the command 'dpkg --configure -a' it fails (because you are not 'root' in that moment).
I agree, it's a bit confusing. The error message should be better.
So adding "sudo" (= execute something as superuser 'root') to that part should allow the command 'dpkg --configure -a' to execute correctly, and then really fix the previous problem.